Di Maria had a game to forget against Sunderland at Old Trafford on Saturday, substituted at half-time as United claimed a 2-0 victory.
After a bright start to life in the Premier League following his British record £59.7 million transfer, the 27-year-old's form has dipped dramatically.
However, Rooney insists it is only a matter of time before Di Maria, who has three goals and eight assists this season, regains his confidence and helps United secure a top-four finish.
"He's a great player, he's shown that and you don't lose your talent overnight," Rooney said.
"Hopefully he'll get back to his best and start giving some great performances for us. He has a lot of experience and I think he'll figure it out – we all have to do that sometimes.
"There's nothing worse than when everyone keeps going on at you. You have to come to it in your own way and I'm sure he'll be a big player for us between now and the end of the season."
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